At present, a liquid flowing substantially horizontally in a tank and undergoing a treatment as it flows, such as for example a decantation or flotation treatment, may be introduced into the tank or extracted from this tank by different means.
First means consist of introducing or extracting the liquid through a pipe opening into the inside of the volume of the tank. This method of introduction or extraction may be improved by using an overflow, i.e. by distributing the introduction or extraction area of the liquid substantially over the entire width of the tank. Throughout the volume of the tank, these introduction or extraction means create preferential areas of flow of the fluid on the one hand and still areas on the other hand, i.e. areas of the volume of the tank where the liquid is substantially static. In fact, the speed of the liquid in the introduction area or extraction area is considerable with regard to the speed of flow of the liquid, for example in the central area of the tank. Consequently, the flow of liquid will tend to develope in an area having the shape of a cone or bevel converging towards the introduction or extraction area of the liquid. Around this preferential area of flow, the liquid will be substantially static, i.e. the preferential area of flow will be surrounded by still areas.
Other means for controlling the flow of a fluid within a tank, where it undergoes a treatment, consist of partitioning-off this tank by perforated walls and of forcing the fluid to flow inside these perforations. Generally, between the walls, oblique partitions define channels which promote the flow and treatment of the liquid. However, the perforations have identical dimensions, which in the volume of the tank causes a flow of the fluid which is not suitable for the treatment which it undergoes, in view of the fact that this flow tends to be substantially uniform throughout the volume of the tank. As an example, we can state that in the case of decantation, the concentration of impurities is greater in the lower part than in the upper part and that for this reason a uniform flow of liquid in the tank is not suitable for the treatment of this liquid. An apparatus of this type is described in U.S. Pat. No. 3,898,164.
One of the objects of the present invention is to propose an apparatus for the treatment of a liquid, flowing in a tank, which makes it possible to determine and control a distribution of speeds of the liquid throughout the entire volume of the tank, which is suitable for the treatment which this liquid undergoes in the tank. According to the invention, the distribution of speeds of the liquid in the tank is determined from the inlet area or from the outlet area, i.e. from the introduction area or from the extraction area of the liquid.
One of the objects of the present invention is thus to determine a distribution of speeds which is suitable for the treatment which the liquid undergoes in the volume of the tank.
Another object of the present invention is to prevent the creation of still areas and preferred areas of flow in the tank, i.e. in fact to optimize the treatment of the liquid in the tank by determining and adapting the distribution of the speeds to the treatment which it undergoes.
Furthermore, it should be noted that the invention relates to the methods and apparatus for the treatment of a liquid flowing substantially horizontally in a tank, whether or not this treatment requires the use of specific treatment means, such as distribution channels or paddles.
The specific treatment means with which the apparatus according to the present invention may be associated have been widely described in the literature of existing patents, in particular in the field of the decantation of liquids. In this respect we can cite British Pat. No. 22,556, U.S. Pat. No. 2,673,451, British Pat. No. 1,042,935, U.S. Pat. No. 3,399,135, British Pat. No. 1,351,801, U.S. Pat. No. 3,666,112, U.S. Pat. No. 3,951,818, U.S. Pat. No. 3,847,813, etc.
Such documents describe specific treatment means such as distribution channels or paddles which facilitate the treatment of the liquid and accelerate it. The apparatus according to the present invention may complement apparatus of this type described in these documents. In fact, specific treatment means of this type cause disturbances in the flow of liquid, which the apparatus according to the present invention is able to compensate or correct from the inlet or outlet. In fact, as will become apparent hereafter, the apparatus according to the invention makes it possible to control the distribution of speeds of the liquid within the tank, from the inlet or outlet and thus to accelerate the liquid in favourable areas, i.e. in areas where the liquid is not treated with maximum efficiency and thus to slow the latter down in unfavourable areas, i.e. areas where the treatment to which the liquid is subjected exceeds saturation.
In the prior art, the overall speed of the liquid was determined in order that the treatment which the liquid undergoes in unfavourable areas is not saturated. On the contrary, in the present case, by modifying the distribution of speeds, all the areas of flow of the liquid in the tank are given speeds such that the treatment which the liquid undergoes is optimum in all these areas.
Generally speaking, the pressure drop which the liquid undergoes in the tank is defined by the difference in levels between the liquid at the inlet and outlet. It is this pressure drop which defines the overall rate of flow of the liquid in the tank. The present invention proposes to control this overall rate of flow by imposing a predetermined speed distribution within the volume of the tank.
It should also be noted that the invention relates not only to the treatment of a liquid by decantation or by flotation, but to all types of treatment of a liquid where it is advantageous to determine and control a distribution of speeds which improves the efficiency of said treatment.